JPS636989B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention improves and stabilizes the moldability when molding the positive electrode active material of a button-type battery, particularly a small and thin button-type battery, into a predetermined shape in a positive electrode container, and increases the electric capacity by increasing the density of the molded product. The present invention relates to a method of manufacturing a positive electrode part. Generally, the positive electrode part of a button type battery is made of positive electrode active material 1
A positive electrode ring 2 is interposed on the upper periphery of the positive electrode ring 2 and is pressurized into the positive electrode container 3 to increase the molding density of the positive electrode active material. This is because the positive electrode ring prevents the pressure applied when sealing the battery, and also prevents the positive electrode from deforming or collapsing due to chemical changes during storage of the positive electrode active material and sealing pressure. Densification has important implications. However, in recent years, as batteries have become smaller and thinner, there has been a need to reduce the thickness of the positive electrode.As the thickness of the positive electrode becomes thinner, the molding density decreases when molded at the same molding pressure. It is necessary to increase the pressure. However, when the thickness of the positive electrode active material is reduced and the pressure is increased to mold it, the center of the positive electrode part is curved as shown in Figure 2, and this curved part of the positive electrode active material causes cracks, peeling, and contact with the positive electrode ring. Along with the occurrence of gaps, the adhesion between the positive electrode part and the positive electrode container becomes weak, and the positive electrode active material may come off during battery assembly, or the electrolyte injected into the positive electrode active material may crack, peel off, or leak from the side wall of the positive electrode container to the outside through gaps. This has led to a tendency for cell creep to occur, resulting in extremely inconvenient aspects in terms of battery productivity and quality. Furthermore, if the pressurizing force is reduced, the occurrence of curvature and cracks in the positive electrode part will be eliminated, but at the same time, the molding density will decrease, and due to the limitation of the thickness of the positive electrode part, the filling amount of the positive electrode active material will decrease, and the electric capacity will decrease. More electrolyte than necessary penetrates into the positive electrode active material,
During storage, the storage performance deteriorated significantly, which caused a decrease in reliability in terms of battery quality. The present invention solves these drawbacks,
As a result of various studies on the moldability of the positive electrode part, we found that during the pressurization process in which the positive electrode ring is bonded to the positive electrode active material roughly formed into pellets in the positive electrode container, it is possible to re-shape it by applying pressure at least twice. death,
In addition, by increasing the pressurization pressure from the second time onwards compared to the first time, the molding density of the positive electrode active material is increased, and curvature of the positive electrode active material is prevented, thereby suppressing the occurrence of cracks, peeling, and gaps. This is what I discovered that can be done. An embodiment of the present invention will be described below with reference to the drawings.
FIG. 1 is a half-sectional view of a thin button battery constructed according to the present invention. A positive electrode active material 1, which is mainly a mixture of monovalent silver oxide and graphite, is roughly molded into a pellet shape, and is press-fitted together with a positive electrode ring 2 into a positive electrode container 3. A separator 4, an electrolyte-impregnated material 5, a negative electrode 6 mainly made of a mixture of zinc chloride powder and a substance that gels in an alkaline electrolyte such as carboxymethyl cellulose, and a sealing ring 7 made of nylon or the like are sandwiched thereon in order. The battery is sealed by placing the negative electrode container 8 that has been prepared and curling the upper end of the positive electrode container inward. Figure 2 shows a cross section of the positive electrode part in the conventional manufacturing method.If the pressurizing force is increased to obtain the required thickness and molding density of the positive electrode part, the center of the positive electrode active material will curve and cracks, peeling, etc. will occur. Occur. This phenomenon occurs because the air contained in the positive electrode active material is not sufficiently degassed during pressure molding, and the residual air expands and the filling amount of the positive electrode active material is small, resulting in a change in thickness H relative to the outer diameter φ of the positive electrode part. As the ratio φ/H increases, the mechanical behavior of the pressure applied to the positive electrode active material differs from that of either gas or liquid, and the force applied to one point cannot be transmitted equally in all directions. As a result, the stress distribution becomes uneven, and the density distribution after molding becomes uneven, or the deformation of powder particles that occurs during the powder compression process becomes incomplete due to uneven pressure stress, resulting in uniform pressure force. This is thought to be caused by residual stress being stored inside the powder. In the present invention, the air contained in the positive electrode active material is sufficiently degassed by performing the pressurization process at the time of molding at least twice and setting the pressurizing force, rather than the conventional one-time molding process. At the same time, by gradually increasing the pressure, the arrangement state of the powder particles can be easily changed, reducing the uneven stress distribution of the pressure, increasing the pressure applied to each powder particle, making it more uniform, and deforming the powder particles. This is to ensure that this is carried out adequately. This reduces the residual stress inside the powder, making it possible to prevent curvature, cracking, and peeling of the positive electrode active material, and also to make the molding density distribution uniform and to achieve high-density molding, that is, to increase the capacity. By the way, the diameter is 11.6m/m and the height is 2.0m/m.
In a silver oxide battery with a diameter of 7.9 m/m and a height of 2.0 m/m, bending, cracking, peeling, etc. of the positive electrode active material after molding when the conventional molding method and the molding method of the present invention and the pressurizing force were changed. Comparing the molding defects and molding density, the results are shown in Table 1. Table 1 shows that when using the conventional molding method, the molding density increases as the pressing force increases, although it varies depending on the type of battery. However, the number of molding defects after molding increases. Further, by performing pressure molding several times with the same pressure, it is possible to increase the density and reduce molding defects, but it cannot be said to be perfect. By successively increasing the pressure setting during molding, it was possible to obtain the required molding density and to reduce the occurrence of molding defects to 0.01% or less. Furthermore, when comparing the conventional molding method and the method of the present invention with the same size of the positive electrode part, the method of the present invention was able to fill 7 to 15% more positive electrode active material than the conventional method. In addition, for batteries with a height higher than 2.0 m/m, molding defects such as curvature of the positive electrode active material hardly occur even if the pressurizing force is 6 to 10 tons, but the molding density is 5.3 to 5.6 m/m. The limit was g/cc. On the other hand, in the pressurizing process of the present invention, a molding density of 5.5 to 6.0 g/cc can be easily obtained by molding with a pressing force of 4 to 6 tons for the first time and 6 to 10 tons for the second time. I was able to do that.

[Table] Next, Table 2 shows the leakage resistance performance of a silver oxide battery with a diameter of 11.6 m/m and a height of 2.0 m/m, which has a positive electrode part manufactured by the method of the present invention. KΩ
Shows the discharge characteristics under constant resistance load. In addition, battery A was pressurized twice, with the first pressurizing force being 2 to 3 tons and the second pressurizing force of 4 to 8 tons, and the molding density was 5.2 g/cc, and battery B was The pressure was applied three times, the first pressurizing force was 2 to 3 tons, the second was 4 to 8 tons, and the third was 6 to 3 tons.
The weight was 10 tons, and the molding density was 5.4 g/cc. Battery C was pressurized by 6 to 8 tons using the conventional method.
The molding density is 5.1g/
It was cc. In addition, the test conditions for leakage resistance are at a temperature of 45
Fifty pieces of each were stored at ℃ and 90% relative humidity.

[Table] By using the present invention as described above, it is possible to sufficiently degas the air contained in the pellet-like positive electrode active material and to improve the flow of powder particles, especially when molding the positive electrode part of a thin alkaline button battery. By reducing non-uniformity of stress distribution, it is possible to reduce defects and increase capacity, and to improve the reliability of storage performance of the battery. Although the above example was explained with respect to a silver oxide battery, it was confirmed that the same effect could be obtained with a divalent silver oxide battery, a mercury battery, and a button-type alkaline manganese battery, although there was a difference in the set pressure. did.

[Brief explanation of the drawing]

Fig. 1 is a half-sectional view of a thin alkaline button battery obtained by the manufacturing method of the present invention, Fig. 2 is a sectional view of the positive electrode part obtained by the conventional manufacturing method, and Fig. 3 is a discharge of the battery by the manufacturing method of the present invention. FIG. 3 is a diagram showing characteristics. 1... Positive electrode active material, 2... Positive electrode ring, 3...
Positive electrode container, 4...Separator, 6...Negative electrode, 8...
...Negative electrode container.

Claims (1)

[Claims] 1. The positive electrode active material is formed into a pellet by rough molding, and a positive electrode ring with an inverted L-shaped cross section is interposed on the upper periphery of the pellet, and the positive electrode ring is inserted into the positive electrode container. The positive electrode container, the positive electrode active material, and the positive electrode ring are then pressurized. A positive electrode part for a thin alkaline button battery, characterized in that the positive electrode part for a thin alkaline button battery is re-molded by applying pressure at least twice or more in the attaching process, and the pressure applied from the second time onwards is greater than the pressure applied at the first time. Manufacturing method.